Some interviewers use the "Take it or leave it" approach.
If you think this interviewer might negotiate, approach
it tactfully.
You might say, "A higher salary would be warranted
because... and then fill in the blank."
If you are unsure that they will negotiate, don't push it.
Tell them you'll think over the offer.
And keep in the back of your mind that if they're this
inflexible about salary, the company might be inflexible
about other important matters as well.